1. Field of the Invention
The present invention relates to a tire condition detection system with various sensors for determining the physical properties inside a tire, such as the air pressure, the temperature and the like, and an induction supply method for externally supplying the power necessary for the operation of the sensors via wires or mesh embedded in the tire rubber to increase the tire strength.
2. Description of the Related Art
Conventionally, the technology relating to tire condition detection systems is as described in, for example, the following documents.
Publication 1: Japanese Patent Application Laid-Open (JP-A) No. 10-104103
Publication 2: JP-A No. 2003-237328
Publication 3: JP-A No. 2003-291615
Publication 4: JP-A No. 2004-161113
In Publication 1 is disclosed technology of a tire pressure monitoring device including a central reception evaluation device placed in a vehicle, and used for a vehicle having plural wheels.
In Publication 2 and 4 is disclosed technology relating to a wireless tire condition monitoring device in which the tire internal air pressure and the like may be confirmed from within the cabin of a vehicle.
In Publication 3 is disclosed technology of a tire air pressure detection device that detects the condition of a tire, such as the air pressure, temperature and the like, and transmits the condition of the tire by wireless signal.
Generally, any antennas follow a so-called reversal theorem, i.e., transmission characteristics are exactly the same as reception characteristics, therefore in the following explanation, transmission will be explained, and, except for particular instances, since reception is the same, explanation thereof will be omitted.
Recently, with computers becoming ultra-small, and the possibility of the use of single chip computers has become a reality, there has been remarkable progress in the technical development of vehicles such as cars and the like. Various communications devices, engine control devices, driving safety devices for assisting the driving operation of a driver, and the like, that are provided in vehicles rely, in the main, on computers, and evolution in the performance/functionality of vehicles continues to develop. With the above, it seems that, apart from specialists, the general public do not seem to recognize the extremely important roll that the wheels perform in supporting and moving the vehicle body.
In the past, it was normal for vehicle wheels to be constructed of a wheel, a tube, and a tire. However, due to the development of tubeless tires, tubeless tires are used on nearly all vehicles, with the exception of heavy vehicles, and so car wheels are constructed of a wheel and a tubeless tire (referred to below as “tire” for simplicity). Since air tubes have disappeared, punctures are not the slow leaking of air as before, but a sudden splitting (bursting), and it is not rare that this leads to a serious traffic accident.
Also, there is a close relationship between tires and the engine mileage, and there is good fuel consumption efficiency when running with the optimum pressure, and it is well known that the distance that can be traveled using a given amount of fuel can be extended. The fact that someone will check your tires when refilling with gasoline at a gas station is for this reason.
Even if the value of the air pressure is optimal for normal driving, when driven for an extended period of time, at a high speed, the air within a tire moves intensely, and the tire also deforms while rotating, so generating a large amount of heat, that may raise the internal temperature of the tire to about 150° C. The result is that, whilst the air pressure within the tire should be at the optimum temperature, the air pressure is actually raised by such generated heat, and this may sometimes lead to the tire exploding.
Due to this, as described in the Publications 1 to 4, and the like, devices have been developed for detecting the air pressure and temperature of tires, and currently, it is obligatory to fit such devices to all new models of car in the United States.
FIGS. 3A and 3B are explanatory diagrams of a conventional tire condition detection system. FIG. 3A is an external view of a vehicle wheel structure and antenna system provided with a conventional tire condition detection system. FIG. 3B is a diagram showing the wheel cross section and reception antenna provided in a tire pressure/temperature detection device of the tire condition detection system of FIG. 3A.
As shown in FIG. 3A, the vehicle body is provided with a vehicle wheel rotating axel 1 for the front wheels, and a vehicle wheel rotating axel 2 for the rear wheels, and respective tires 10 are mounted via wheels 3 on these vehicle wheel rotating axels 1, 2. Each of the wheels 3 on which each of the tires 10 are mounted has a valve 20 with an air ingress and egress aperture, and accommodated in each of the valves 20 is a small, tag-shaped tire pressure/temperature detection device. The small tag-shaped tire pressure/temperature detection device is configured with a sensor for detecting the internal pressure and temperature of the tire 10, an IC tag of an integrated circuit for overall control of the device, an internal antenna for use in transmitting and receiving electromagnetic waves R, a battery for use in driving the device, and the like.
A reader antenna 40, as an external antenna for transmitting and receiving data and commands from internal antennae of each of the valves 20, is fitted to the vehicle body. The reader antenna 40 is connected to a reader-writer (referred to below as R/W) 42 via a transmission path 41 of a coaxial cable or the like. The R/W 42 is driven by high frequency power supplied by the high frequency power source 43, is a device for processing all of the data relating to the tire pressure/temperature detection devices inside all of the valves 20, and is connected to a display device 44. The display device 44 is installed in the vehicle cabin, and is a device for displaying to the driver incoming information relating to the physical condition of the tire 10 that is sent from the R/W 42.
As shown in FIG. 3B, the valve 20 accommodating the tire pressure/temperature detection device is fixed to the wheel 3, and a ring shaped tire 10 is mounted to the outer peripheral surface of the wheel 3 in a removable state. In the tire 10 is embedded metal wire or metal mesh formed from steel material or the like, as reinforcement material 13 for increasing the tire strength. Electromagnetic waves R, transmitting data of the internal air pressure and temperature of the tire 10, are radiated from the internal antenna of the valve 20, and these electromagnetic waves R are received by the reader antenna 40, the received signal is processed by the R/W 42, and values of the air pressure and temperature within the tire 10 are displayed on the display device 44.
FIGS. 4A and 4B are block diagrams of the valve 20 of FIGS. 3A and 3B. FIG. 4A is an external view of the front of the valve 20. FIG. 4B is an external view of the back thereof.
The valve 20 has a case shaped valve body 21 that opens to the back side thereof, and accommodates the tire pressure/temperature detection device, and at a side face of the valve body 21 protrudes a cylindrical shaped air egress and ingress aperture 22. The air egress/ingress aperture 22 is made of a strong metal, for example aluminum alloy or steel, and the rest of the valve body is made from a resin or the like. An air passage hole 23 is formed in the valve body 21 for communicating to the inside of the tire 10 from the air egress/ingress aperture 22. The opening portion at the back of the valve body 21 is constructed to be closed off with a back cover 24, protecting internal portions of the device, so that the device does not fall out of the valve body 21. On the cover 24 is formed a post 25 for positional alignment of the valve body and the back cover 24.
FIG. 5 is an internal block diagram of the valve 20 of FIGS. 4A, B as seen when the back cover 24 has been removed.
Accommodated in the valve body is a button battery 26 for supplying power, and a tire pressure/temperature detection device 30 connected to the button battery 26, via a transmission path 27 of conductive wire of the like. The tire pressure/temperature detection device 30 has a substrate 31 for mounting circuit elements. On the substrate 31 are mounted an air pressure sensor 32, a temperature sensor 33, an electrical circuit 34, for processing data and overall control of the device, and the electrical circuit 34 is connected to the transmitting antenna 35 that is the internal antenna.
By the mechanism of such a tire pressure/temperature detection device 30, it is possible for a driver, seated in the driver's seat or while driving, to know the air pressure and temperature inside of the tire 10. Since a critical cause of bursting of the tire 10 is the internal air pressure and temperature thereof, if the driver undertakes suitable measures when the condition of the tire 10 becomes dangerous, then a tire explosion and traffic accident may be avoided before they happen.
FIG. 6 is an explanatory diagram of the structure of the tire 10 in FIGS. 3A and B.
The tire 10 has a ring shaped rubber portion 11, and on the inside of the rubber portion 11 is formed a levering portion 12 for levering the tire 10 onto the wheel 3 when mounting. Reinforcement material 13 of metal wire or mesh formed from steel material or the like is embedded in the rubber portion 11 for increasing the tire strength. The cross-section 13a of the reinforcement material 13 looks like loop shaped wire as shown in FIG. 6. There are various ways of arranging the reinforcement material 13, depending on the tire manufacturer, and FIG. 6 shows the simplest arrangement.
However, conventional tire condition detection systems provided with the tire pressure/temperature detection device 30 have the following problems.
The power source of the tire pressure/temperature detection device 30 is the dry button battery 26, and the power of the button battery 26 continuously depletes from the time of insertion into the device. From the specifications of the tire pressure/temperature detection devices 30 on the market, the button battery 26 should be able to continue to supply power to the devices for 10 years or more, but there are hardly any batteries from the button batteries 26 currently on the market that are able to satisfy such a specification. Therefore, in order to slow down the power depletion of the button batteries 26, measures are undertaken, such as, for example, only transmitting data on the air pressure and temperature of the tire 10 to the reader antenna 40 once every 3 minutes or so. But even by taking these measures, it is difficult to prolong the life of the button battery 26 to 10 years.
As another method it is possible to change over to a new battery when the button battery 26 depletes, but more than the cost of the batteries themselves there is the time and expense of changing them over, and there is a problem of damage occurring when changing over tubeless tires and the like, reducing the life of the tire 10. Also, when it is necessary to detect the air pressure and temperature inside the tire 10 at small intervals, such as, for example, transmitting data once every second, a 10 year life battery lasts about 2 or 3 months, and it is obvious that conventional tire condition detection systems are not able to meet the demands of such a specification.